I know this link is for Ubuntu 5.10, but it worked in 6.06 for my 17'' CRT. Now Ubuntu recognizes all the resolutions and refresh rates that my monitor can handle.

http://www.ubuntuforums.org/showthread.php?t=83973

Scroll down to ''How to reconfigure Xorg.'' I do the whole X configuration process. Make sure that the correct video card family is selected. Enter your horizontal and vertical refresh rates manually (find them in your monitor's manual). If you are not sure about certain settings, use the defaults.

Hope this helps.